lec10, video i (basics of analog and digital video), v1.03.ppt

Multimedia SystemsMultimedia Systems

Video IVideo I

(Basics of Analog and Digital Video)(Basics of Analog and Digital Video)

Course PresentationCourse Presentation

(Basics of Analog and Digital Video)(Basics of Analog and Digital Video)

Mahdi Amiri

April 2014

Sharif University of Technology

VideoVisual Effect of MotionVisual Effect of Motion

The visual effect of motion is due to biological phenomenons.

1. Persistence of vision

An object seen by the human eye remains

mapped on the eye’s retina for a brief time

after viewing (approximately 25 ms)

2. Phi phenomenon

Multimedia Systems, Mahdi Amiri, Video IPage 1

2. Phi phenomenon

When two light sources are close by and they are

illuminated in quick succession, what we see is not two

lights but a single light moving between the two points

(apparent movement

or perceiving movement)

Due to the above two phenomena of our vision system, a

discrete sequence of individual pictures can be perceived as a

continuous sequence.

VideoDefinitionDefinition

A sequence of still images representing scenes in motion.

Frame Rate

Number of still images/pictures per unit time

Frames / Second (fps)Frame N-1


Frame rate of video ranges from 6 to 8 fps

for old mechanical cameras to 120 or

more fps for new professional cameras.

The minimum frame rate to achieve

illusion of a moving image is 15 fps. Frame 0TimeTime

Video RepresentationVideo Display, CRTVideo Display, CRT

In conventional TV sets or monitors, the video signal is displayed using a

CRT (Cathode Ray Tube).

An electron beam sweeps the screen from top to bottom beam carrying the

corresponding pattern information, such as intensity in a viewed scene.

Video can be interlaced or progressive ( Will be discussed later in this lecture ).


Video RepresentationVideo Display, LCDVideo Display, LCD

Millions of LCD shuttersen.wikipedia.org/wiki/LCD_television

Liquid-crystal-display televisions (LCD TV) produce a black and colored image by selectively

filtering a white light. The light is typically provided by a series of cold cathode fluorescent lamps

(CCFLs) at the back of the screen, although some displays use white or colored LEDs instead.

Millions of individual LCD shutters, arranged in a grid, open and close to allow a metered amount

of the white light through. Each shutter is paired with a colored filter to remove all but the red, green

or blue (RGB) portion of the light from the original white source.


electronics.howstuffworks.com/lcd2.htm

If we apply an electric charge to liquid crystal molecules, they untwist. When they straighten out, they change the angle

of the light passing through them so that it no longer matches the angle of the top polarizing filter. Consequently, no

light can pass through that area of the LCD, which makes that area darker than the surrounding areas.

Video DisplayProgressive ScanningProgressive Scanning

Flicker free at around 50 frames per second (fps)

FlickerFlicker is a visible fading between is a visible fading between

cycles displayed on video displays, cycles displayed on video displays,

especially the refresh interval on especially the refresh interval on

cathode ray tube (CRT) based cathode ray tube (CRT) based


cathode ray tube (CRT) based cathode ray tube (CRT) based

computer screens.computer screens.

Flicker and BandwidthFlicker and Bandwidth

Video DisplayInterlaced ScanningInterlaced Scanning

First the solid (odd) lines are traced, P to Q, First the solid (odd) lines are traced, P to Q,

then R to S, etc., ending at T; then the even then R to S, etc., ending at T; then the even

Field starts at U and ends at V.Field starts at U and ends at V.

Flicker free at around 25 frames per second (fps)


The jump from Q to R, etc. is called the The jump from Q to R, etc. is called the

horizontal retracehorizontal retrace, during which the , during which the

electronic beam in the CRT is blank.electronic beam in the CRT is blank.

The jump from T to U or V to P is called The jump from T to U or V to P is called

the the vertical retracevertical retrace..

Electronic signal for Electronic signal for

one NTSC scan line.one NTSC scan line.

Video DisplayOdd and Even FieldsOdd and Even Fields

OddOdd

FieldField


EvenEven

FieldField

Difference Difference

of Fieldsof Fields

A Video FrameA Video Frame

Because of interlacing, the odd and even lines are displaced in Because of interlacing, the odd and even lines are displaced in

time from each other time from each other -- generally not noticeable generally not noticeable except when except when

very fast action is taking place very fast action is taking place on screen, when blurring may on screen, when blurring may

occur.occur.

InitiallyInitially the the oddodd--numbered lines are scanned and numbered lines are scanned and thenthen the the

process is repeated for process is repeated for eveneven--numbered lines numbered lines -- this time this time

starting at the second row.starting at the second row.

Video DisplayDeinterlacingDeinterlacing

Deinterlacing is the process of converting interlaced video, such as

common analog television signals into a non-interlaced form.

Method 1: Capturing one field and combining it with the next field

Problem: "combing" effect

Method 2: Line doubler


When interlaced video is watched on a When interlaced video is watched on a

progressive monitor with very poor progressive monitor with very poor

deinterlacingdeinterlacing, it exhibits combing when there , it exhibits combing when there

is movement between two fields of one frame.is movement between two fields of one frame.

Method 2: Line doublerThe most basic and literal way to double lines is to repeat each The most basic and literal way to double lines is to repeat each

scanlinescanline, though the results of this are generally very crude. , though the results of this are generally very crude.

Most line doublers use digital interpolation to recreate the Most line doublers use digital interpolation to recreate the

missing lines in an interlaced signal, and the resulting quality missing lines in an interlaced signal, and the resulting quality

depends on the technique used. Generally a line depends on the technique used. Generally a line doublerdoubler will will

only only interpolate within a single fieldinterpolate within a single field, rather than merging , rather than merging

information from adjacent fields, to preserve the smoothness information from adjacent fields, to preserve the smoothness

of motion, resulting in a frame rate equal to the field rate.of motion, resulting in a frame rate equal to the field rate.

Serrated imageSerrated image

Analog Broadcast TV SystemsNTSCNTSC

NTSC (National Television System Committee)

Mostly used in North America and Japan

Aspect Ratio: 4:3


525 scan lines at 30 fps

Interlaced scanning (262.5 lines/field)

Color Space: YIQ

Analog Broadcast TV SystemsYIQ Color SpaceYIQ Color Space

In the YIQ color system, the I axis runs from cyan to

orange, and the Q axis runs from green to violet.

Eye is most sensitive to Y, next to I, next to Q.

Bandwidth allocation for color components

4 MHz is allocated to Y,

1.5 MHz to I,


1.5 MHz to I,

0.6 MHz to Q.

When compared to PAL in particular, NTSC color

accuracy and consistency is sometimes considered

inferior, leading to video professionals and television

engineers jokingly referring to NTSC as Never The

Same Color, Never Twice the Same Color, or No True

Skin Colors,[16] while for the more expensive PAL

system it was necessary to Pay for Additional Luxury.

Analog Broadcast TV SystemsPALPAL

PAL (Phase Alternating Line)

Mostly used in Western Europe, China and India

Aspect Ratio: 4:3




Interlaced scanning (312.5 lines/field)

Color Space: YUV

5.5 MHz is allocated to Y, 1.8 MHz each to U and V.

Analog Broadcast TV SystemsSupplementary MaterialsSupplementary Materials

The horizontal sweep frequency is

525×30 ≈ 15,750 lines/sec, so that each

line is swept out in 1/15,750 sec ≈

63.5µsec.

Vertical retrace takes place during 20

lines reserved for control information at

NTSC Video Signal


A typical waveform of a NTSC composite video signal

lines reserved for control information at

the beginning of each field. Hence, the

number of active video lines per frame is

only 485.

Similarly, almost 1/6 of the raster at the

left side is blanked for horizontal retrace

and sync. The nonblanking pixels are

called active pixels.

NTSC video is an analog signal with no

fixed horizontal resolution. Therefore one

must decide how many times to sample

the signal for display: each sample

corresponds to one pixel output.


An NTSC television channel as transmitted occupies a

total bandwidth of 6 MHz

Modulation of NTSC

The actual video signal, which is amplitude-modulated, is

transmitted between 500 kHz and 5.45 MHz above the

lower bound of the channel. The video carrier is 1.25 MHz

above the lower bound of the channel. Like most AM


Spectrum of a System M television channel with NTSC color.

above the lower bound of the channel. Like most AM

signals, the video carrier generates two sidebands, one

above the carrier and one below. The sidebands are each

4.2 MHz wide. The entire upper sideband is transmitted,

but only 1.25 MHz of the lower sideband, known as a

vestigial sideband, is transmitted.

The color subcarrier, as noted above, is 3.579545 MHz

above the video carrier, and is quadrature-amplitude-

modulated with a suppressed carrier.

The audio signal is frequency-modulated.


Chroma Modulation of NTSC

In NTSC, chrominance (C) is encoded using two

3.579545 MHz signals that are 90 degrees out of phase,

known as I (in-phase) and Q (quadrature) QAM. These

two signals are each amplitude modulated and then

added together.

( ) ( ) ( ) ( ) ( )0 0cos 2 sin 2C t I t f t Q t f tπ π= +

0 is the carrier frequencyf


In the ideal case I(t) is demodulated by multiplying the

transmitted signal with a cosine signal.

Chroma Demodulation of NTSC

( ) ( ) ( )( ) ( ) ( ) ( ) ( ) ( )( ) ( ) ( )( ) ( ) ( )( ) ( ) ( ) ( ) ( ) ( )

0

2

0 0 0

0 0

0 0

2cos 2

2 cos 2 2 sin 2 cos 2

1 cos 4 sin 4

cos 4 sin 4

i

i

i

i

r t C t f t

r t I t f t Q t f t f t

r t I t f t Q t f t

r t I t I t f t Q t f t

π

π π π

π π

π π

= ⋅

= +

= + +

= + + Low-pass filtering ri(t) removes the high frequency terms

(containing 4πf0t), leaving only the I(t) term.

Similarly, Q(t) can be extracted by first multiplying C(t)

by 2sin(2πf0t) and then low-pass filtering.


The basics of PAL and the NTSC system are very similar;

a quadrature amplitude modulated subcarrier carrying the

chrominance information is added to the luminance video

signal to form a composite video baseband signal.

Modulation of PAL

In order to improve picture quality, chroma signals have

alternate signs (e.g., +U and -U) in successive scan lines,


Spectrum of a System I television channel with PAL color.

alternate signs (e.g., +U and -U) in successive scan lines,

hence the name “Phase Alternating Line”. This facilitates

the use of a (line rate) comb filter at the receiver —the

signals in consecutive lines are averaged so as to cancel

the chroma signals (that always carry opposite signs) for

separating Y and C (chroma) and obtaining high quality

Y signals;

However, this resulted in a comblike effect known as

Hanover bars on larger phase errors. Thus, most receivers

now use a chrominance delay line, which stores the

received color information on each line of display; an

average of the color information from the previous line

and the current line is then used to drive the picture tube.Hanover bars Cancellation of Hanover bars

through a chroma delay line


SECAM stands for Système Electronique Couleur Avec

Mémoire, the third major broadcast TV standard.

Aspect Ratio: 4:3

625 scan lines at 25 fps, Interlaced scanning


625 scan lines at 25 fps, Interlaced scanning

SECAM and PAL are very similar. They differ

slightly in their color coding scheme:

In SECAM, U and V signals are modulated using separate

color subcarriers at 4.25 MHz and 4.41 MHz respectively.

They are sent in alternate lines, i.e., only one of the U or V

signals will be sent on each scan line.


.


More at

http://en.wikipedia.org/wiki/Broadcast_television_systems

Analog Color VideoSignal ProtocolsSignal Protocols

Composite video

1956

1 wire

Color (chrominance) and luminance

signals are mixed into a single carrier wave.


signals are mixed into a single carrier wave.

Since color and intensity are wrapped

into the same signal, some interference

between the luminance and chrominance

signals is inevitable.

Composite video jacks are often grouped

with corresponding stereo audio jacks (the

composite video jack is usually yellow)


S-Video (Separated video, e.g., in S-VHS)1979

2 wires, one for luminance and another for composite

chrominance signal

As a result, there is less crosstalk between the color information


As a result, there is less crosstalk between the color information

and the crucial gray-scale information.

A compromise between component analog video and the

composite video.

A standard 4A standard 4--pin Spin S--Video cable Video cable

connector, with each signal pin (3, 4) connector, with each signal pin (3, 4)

paired with its own ground pin (1,2)paired with its own ground pin (1,2)


Component video1990

3 wires

Each primary is sent as a separate video signal. The primaries

can either be RGB or a luminance-chrominance transformation of


can either be RGB or a luminance-chrominance transformation of

them (e.g., YPbPr, YIQ, YUV).

Y: Green wire, Pb: Blue wire, Pr: Red wire

Best color reproduction

Requires more bandwidth and good

synchronization of the three components

More about signal protocols atMore about signal protocols at

http://en.wikipedia.org/wiki/List_of_display_interfaceshttp://en.wikipedia.org/wiki/List_of_display_interfaces

YPbPr is analog

form of YCbCr

VGA: like component

video using RGB

instead of YPbPr.

Digital VideoAdvantagesAdvantages

Video can be stored on digital devices or in memory,

ready to be processed (noise removal, cut and paste, etc.),

and integrated to various multimedia applications.

Direct access is possible, which makes nonlinear video

editing achievable as a simple, rather than a complex, task.


editing achievable as a simple, rather than a complex, task.

Repeated recording does not degrade image quality.

Ease of encryption and better tolerance to channel noise.

Digital VideoHDTV vs. Conventional TVHDTV vs. Conventional TV

HDTV has higher resolution

1280 × 720 or 1920 × 1080.

HDTV has a much wider aspect ratio of 16:9 instead of

4:3.


4:3.

16:9 is closer to aspect ratio of the human eye sight

HDTV moves toward progressive (non-interlaced) scan.

The rationale is that interlacing introduces serrated

edges to moving objects and flickers along horizontal

edges.

Digital VideoHDTV Display ResolutionsHDTV Display Resolutions

720pReferred to in marketing materials as “HD”

1280×720, progressive scan

0.9 megapixels

1080p


1080pReferred to in marketing materials as “Full HD”


2.0 megapixels

1080i1920×1080, interlaced scan

Aspect Ratio for all is Aspect Ratio for all is

16:9 (W:H)16:9 (W:H)

Digital VideoUU--HDTV Display ResolutionsHDTV Display Resolutions

4K (2160p)

Referred to in marketing materials as “4K Ultra HDTV”


8.3 megapixels

8K (4320p)


8K (4320p)

Referred to in marketing materials as “8K Ultra HDTV”


33.2 megapixels

See World’s first 8K TV See World’s first 8K TV

demonstration.demonstration.

Zoom outZoom out

��

Digital Color VideoSignal ProtocolsSignal Protocols

SDI (Serial Digital Interface), 1989

Standardized by SMPTE (The Society of

Motion Picture and Television Engineers)

For standard definition applications the most

commonly used bit rates is 270 Mbit/s.


commonly used bit rates is 270 Mbit/s.

1998: HD-SDI (high-definition SDI), nominal

data rate of 1.485 Gbit/s.

2002: Dual Link HD-SDI, 2.970 Gbit/s over two

wires

These bit-rates are sufficient for 1920×1080

@ 60 fps

en.wikipedia.org/wiki/Serial_Digital_Interface

Serial digital interface uses

BNC connectors.


DVI (Digital Visual Interface), 1999

Analog and Digital

Max. 1.65 Gbit/sec

2560 × 1600 @ 60 fps

3840 × 2400 @ 33 fps


3840 × 2400 @ 33 fps

HDMI (High-Definition Multimedia Interface), 2003

Uses a pixel based data stream

v1.0 (Dec. 2002) : Max. 1.65 Gbit/sec

1920×1080 @ 60 fps

v1.4 (May. 2009) : Max. 3.4 Gbit/sec

2560 × 1600 @ 75 fps

4096 × 2160 @ 24 fps

en.wikipedia.org/wiki/HDMI


DisplayPort, 2007

Uses a packetized data protocol often used in high-speed data communications.

This provides a faster data rate over the same number of wires.

2560 × 1600 @ 75

1.6 or 2.7 Gbit/sec


1.6 or 2.7 Gbit/sec

DisplayPort:

Support for cables up to 15m long.

Digital Color VideoSignal Protocols, AdaptersSignal Protocols, Adapters

An adapter with HDMI (male)


Picture of a DisplayPort to DVI adapter after

removing its enclosure. The chip on the board

converts the voltage levels generated by the

dual-mode DisplayPort device to be compatible

with a DVI monitor.

An adapter with HDMI (male)

and DVI (female) connectors

An adapter with DVI and

HDMI (female) connectors

For more information and having a list of physical video connectors, see: en.wikipedia.org/wiki/List_of_video_connectors

DisplayPort® to HDMI®

Video Adapter Converter

Digital Color VideoSignal Protocols vs. ConnectorsSignal Protocols vs. Connectors

Note: our focus was to talk about

protocols and not connectors.

e.g. SCART is a connector for analog video

transmission and can use composite, S-

Video and composite video signal protocols.


VGA connector (DE-15 is a common variant.) Became a nearly

ubiquitous analog computer display connector after first being

introduced with IBM x86 machines. Older VGA connectors

were DE-9 (9-pin). The modern DE-15 connector can carry

Display Data Channel to allow the monitor to communicate with

the graphics card, and optionally vice versa.

SCART: Carries stereophonic sound (analog),

along with composite video and/or RGB video.

Some devices also support S-Video, which shares

the same pins as composite video and RGB.

YPBPR is also sometimes supported as a non-

standard extension via the RGB pins.

Thank You

Multimedia SystemsMultimedia Systems

Video I (Basics of Analog and Digital Video)Video I (Basics of Analog and Digital Video)


Thank You

1. http://ce.sharif.edu/~m_amiri/

2. http://www.dml.ir/

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